The present disclosure relates to protective coatings and, more particularly, to a ceramic structure thermal spray bonded to a substrate.
Gas turbine engines typically include a compressor section to pressurize airflow, a combustor section to burn a hydrocarbon fuel in the presence of the pressurized air, and a turbine section to extract energy from the resultant combustion gases. Components that are exposed to high temperatures, such as those within a gas path of the gas turbine engine, typically include protective coatings. For example, components such as turbine blades, turbine vanes, blade outer air seals (BOAS), and compressor components (e.g., floatwall panels) typically include one or more coating layers that function to protect the component from erosion, oxidation, and corrosion or the like to enhance component durability and maintain efficient operation.
As one example, some conventional turbine blade outer air seals (BOAS) include an abradable ceramic coating that contacts tips of the turbine blades such that the blade tips abrade the coating upon engine operation. The abrasion between the BOAS and the blade tips provide a minimum clearance between these components such that gas flow around the tips of the blades is reduced to maintain engine efficiency.
The thermal barrier coatings required for next generation BOAS s are required to demonstrate a high level of durability in the ever increasing temperature's in next generation turbines. Although effective, present thermal barrier coatings are limited to about 2500-2800 F (1371-1537 C) surface temperatures due to sintering induced spallation. Current development coating solutions include geometrically segmented ceramic (GSAC) where metallic surface features cause segmentation of the thermal barrier coating during deposition.
The GSAC coating provides durability at surface temperatures in the vicinity of 3000 F (1649 C) but the metallic substrate features are still limited to about 2000 F (1093 C) to prevent oxidation induced spallation. This may be particularly relevant to BOAS applications where the engine run coating thickness varies substantially after rub interaction. This may cause the 2000 F (1093 C) design limitation to be violated in rubbed areas, while higher initial thickness would violate surface temperature limitations.